Direct-positive silver halide emulsion fogged with low levels of reduction and gold fogging agents

Abstract

Very high speed direct-positive photographic emulsions comprising silver halide grains fogged with both reduction and gold fogging agents are described. For some applications other fogging agents, e.g. compounds of metals more electropositive than silver, can be substituted for the gold fogging agent. Photographic elements employing such emulsions and processes for preparing them are also disclosed.

I claim: 
     
       1. A direct-positive, photographic emulsion which comprises fogged silver halide grains and an organic desensitizer which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of: Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter.   
     
     
       2. The photographic emulsion of claim 1 in which the grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent. 
     
     
       3. The photographic emulsion of claim 1 in which the silver halide comprises at least 50 mole percent bromide and the silver halide grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent, the ratio of gold fogging agent to reduction fogging agent being in the range of about 1:3 to about 20:1. 
     
     
       4. The photographic emulsion of claim 1 in which the silver halide grains have an average grain size less than about 1 micron and are fogged with a reduction fogging agent and a gold fogging agent. 
     
     
       5. The photographic emulsion of claim 1 in which the silver halide grains have an average grain size of less than about 1 micron, are fogged with a reduction fogging agent and a gold fogging agent and said desensitizer is an organic compound which spectrally sensitizes in the range of about 480 to about 800 mμ. 
     
     
       6. The photographic emulsion of claim 2 in which said desensitizer is a cyanine dye. 
     
     
       7. The photographic emulsion of claim 1 which contains a spectral sensitizing dye in addition to said desensitizer. 
     
     
       8. The photographic emulsion of claim 2 in which said desensitizer is an imidazoquinoxaline dye. 
     
     
       9. The photographic emulsion of claim 6 in which the silver halide is silver bromoiodide comprising at least 50 mole percent bromide and less than about 10 mole percent iodide. 
     
     
       10. A photographic element comprising a support and at least one photographic silver halide layer which comprises fogged silver halide grains and an organic desensitizer which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of: Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Distilled water to 1 liter.   
     
     
       11. The photographic element of claim 10 in which the silver halide grains are fogged with a reduction fogging agent and a gold fogging agent. 
     
     
       12. The photographic element of claim 11 in which the concentration of gold fogging agent is in the range of about 0.001 to about 0.01 millimole per mole of silver halide. 
     
     
       13. The photographic element of claim 11 in which the silver halide comprises at least 50 mole percent bromide and the silver halide grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of the reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of the gold fogging agent. 
     
     
       14. The photographic element of claim 10 in which the silver halide is silver bromoiodide comprising at least 50 mole percent bromide and up to about 10 mole percent of iodide. 
     
     
       15. The photographic element of claim 11 in which the photographic silver halide layer is a gelatin photographic silver halide layer. 
     
     
       16. The photographic element of claim 10 in which the silver halide grains are fogged with a reduction fogging agent and a gold fogging agent, the photographic silver halide layer is a gelatin photographic silver halide layer and the silver halide grains have an average grain size up to about 1 micron. 
     
     
       17. The photographic element of claim 10 in which the silver halide grains are fogged with a reduction fogging agent and a gold fogging agent and said desensitizer is an organic compound which spectrally sensitizes in the range of about 480 to about 800 mμ and comprises, contiguous to the silver halide grains, a color-forming coupler. 
     
     
       18. The photographic element of claim 10 in which the silver halide grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide or a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent, the ratio of gold fogging agent to reduction fogging agent tbeing in the range of 1:3 to about 20:1, the silver halide comprises at least about 50 mole percent bromide and said desensitizer is a cyanine dye. 
     
     
       19. The photographic element of claim 18 in which the cyanine dye is an imidazoquinoxaline dye. 
     
     
       20. The photographic element of claim 18 in which the silver halide is a silver bromoiodide which comprises at least 50 mole percent bromine and up to about 10 mole percent iodine. 
     
     
       21. The photographic element of claim 18 in which the reduction fogging agent is thiourea dioxide and the gold fogging agent is potassium chloroaurate. 
     
     
       22. The photographic element of claim 18 in which the reduction fogging agent is thiourea dioxide, the gold fogging agent is potassium chloroaurate and the silver halide is silver bromoiodide which comprises at least 50 mole percent bromine and up to about 10 mole percent iodine. 
     
     
       23. The process which comprises contacting silver halide grains with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.001 millimole per mole of silver halide of a gold fogging agent at a temperature in the range of about 40° to about 100° C., the ratio of gold fogging agent to reduction fogging agent being in the range of about 1:3 to about 20:1. 
     
     
       24. The process of claim 23 in which the silver halide comprises at least 50 mole percent bromide. 
     
     
       25. The process of claim 23 in which the silver halide has an average grain size up to about 1 micron. 
     
     
       26. The process of claim 23 in which the silver halide grains are contacted with the reduction fogging agent and are subsequently contacted with the gold fogging agent. 
     
     
       27. The process of claim 23 in which the reduction fogging agent is thiourea dioxide and the gold fogging agent is potassium chloroaurate. 
     
     
       28. The process of claim 23 comprising adding a desensitizer compound to the silver halide grains after they have been contacted with the reduction and gold fogging agents. 
     
     
       29. Fogged, photographic silver halide grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of: Potasssium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter.   
     
     
       30. The photographic silver halide grains of claim 29 fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent. 
     
     
       31. The photographic silver halide grains of claim 29 in which the silver halide comprises at least 50 mole percent bromide and the grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent, the ratio of gold fogging agent to reduction fogging agent being in the range of about 1:3 to about 20:1. 
     
     
       32. The photographic silver halide grains of claim 31 having an average grain size less than about one micron. 
     
     
       33. The photographic silver halide grains of claim 29 wherein said grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent and having an organic desensitizer compound adjacent said grains which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum. 
     
     
       34. A direct-positive, photographic emulsion which comprises fogged silver halide grains and a desensitizer which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of: Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iadd. 35. The photographic emulsion of claim 1 in which said grains are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer has a maximum density which is at least about 60% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iaddend..Iadd. 36. The photographic element of claim 10 in which said grains are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 60% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iaddend. .Iadd. 37. The fogged photographic silver halide grains of claim 29 in which said grains are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 60% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iaddend..Iadd. 38. The photographic emulsion of claim 34 in which said grains are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-60 developer, has a maximum density which is at least about 60% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iaddend. .Iadd. 39. A direct-positive photographic emulsion which comprises an electron acceptor in combination with fogged silver halide grains wherein at least 95% by weight or by number of the silver halide grains are of a size which is within about 40% of the mean grain size, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iaddend..Iadd. 40. The photographic emulsion of claim 39 in which said grains are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 60% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Potassium bromide--119 mg.   Water to 1 liter. .Iaddend. .Iadd. 41. The photographic emulsion of claim 39 wherein said silver halide grains are reduction and gold fogged. .Iaddend..Iadd. 42. The photographic emulsion of claim 39 wherein the slver halide is silver bromoiodide comprising at least 50 mole percent bromide and up to about 10 mole percent iodide. .Iaddend..Iadd. 43. The photographic emulsion of claim 39 wherein said silver halide grains are cubic. .Iaddend..Iadd. 44. The photographic emulsion of claim 39 wherein said silver halide emulsion contains a spectral sensitizing dye. .Iaddend..Iadd. 45. The photographic emulsion of claim 39 wherein said silver halide emulsion contains a desensitizer which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum. .Iaddend..Iadd. 46. The photographic emulsion of claim 39 wherein said slver halide emulsion contains a color-forming coupler. .Iaddend..Iadd. 47. A direct-positive photographic element comprising a support and at least one photographic silver halide emulsion layer which comprises an electron acceptor compound and reduction and gold fogged, cubic silver halide grains in which said silver halide is silver bromoiodide comprising at least 50 mole percent bromide and up to about 10 mole percent iodide and at least 95% by weight or by number of the silver halide grains being of a size which is within about 40% of the mean grain size, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68° F. in Kodak DK-50 developer, has a maximum density which is at least about 60% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68° F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68° F. in a bleach composition of:   Potassium cyanide--50 mg.   Acetic acid (glacial)--3.47 cc.   Sodium acetate--11.49 g.   Poassium bromide--119 mg.   Water to 1 liter. .Iaddend..Iadd. 48. A direct-positive photographic element according to claim 47 wherein said silver halide emulsion contains a dye-forming coupler and a spectral sensitizing dye. .Iaddend..Iadd. 49. A direct-positive photographic element according to claim 47 wherein said silver halide emulsion contains an organic desensitizer which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum. .Iaddend.